Helsinki tests whether flying squirrels use costly crossing poles

Yle reports that researchers in Helsinki are using fur traps to find out whether flying squirrels use poles installed to help them cross major roads. The study is the first of its kind in Finland.

Near the busy Haaga roundabout, flying squirrels may need to glide 50 to 60 metres from one forested island to another. Roads and a construction site for a new tram line lie between the islands.

The Länsiratikat tram project has installed temporary crossing poles halfway along the route. About 15 permanent poles will eventually be placed at different points in the area to support the squirrels’ movement while newly planted trees grow.

The poles are trimmed pine trunks fixed to concrete bases. Black, tube-shaped fur traps have been attached to some of the poles and to several trees. Ten traps have been installed at a height of about eight metres.

The traps are baited with unsalted peanut butter. Nuts, birch catkins and rowan berries are also possible bait. When a flying squirrel reaches for the food, some of its fur should stick to an adhesive strip inside the trap.

The fur samples will be sent to the University of Oulu for microscopic examination. The traps will be checked about once a month, and the study will continue for at least two years.

Flying squirrels have been seen within about 100 metres of the tram construction site. Crossing poles have been installed in connection with major transport projects in different parts of Finland for several years, but there is no reliable evidence that squirrels use them to cross roads.

“Because there is no previous evidence in Finland that flying squirrels use crossing poles, our aim is to find out whether they are a solution that works for the animals,” said Lotta Siltanen, a landscape designer at the planning consultancy Sitowise.

Siltanen said the method is not certain to detect every animal, as a flying squirrel could pass the trap. If no samples are collected, the project may reconsider the placement of the traps and install several on each pole and tree instead of one.

The tube-shaped traps used in Pitäjänmäki were ordered from an online shop in the United Kingdom specialising in natural science literature and conservation research equipment. Ten traps cost £75, or about 87 euros including postage and customs.

Tuomas Lahti, a senior inspector at the Permits and Supervision Agency, said the use of crossing poles has been justified by experience from other countries. According to Lahti, local species have been proven to use such poles in Japan, Australia and North America. The agency plans to require monitoring in future permit conditions to establish whether squirrels use the poles.